# LeetCode: 1302. Deepest Leaves Sum

## 题目¶

Given a binary tree, return the sum of values of its deepest leaves.

Example 1:

```Input: root = [1,2,3,4,5,null,6,7,null,null,null,null,8]
Output: 15
```

Constraints:

• The number of nodes in the tree is between 1 and 10^4.
• The value of nodes is between 1 and 100.

## 解法¶

```# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
def deepestLeavesSum(self, root: TreeNode) -> int:
self._max_depth = 0
self._sum = 0
self._preorder(root, 0)

return self._sum

def _preorder(self, root, current_deepth):
if root is None:
return

# 将最深的节点值详见
if current_deepth == self._max_depth:
self._sum += root.val

# 发现更深的节点，更新 max_depth 信息同时重置 sum 的值
if current_deepth > self._max_depth:
self._max_depth = current_deepth
self._sum = root.val

self._preorder(root.left, current_deepth + 1)
self._preorder(root.right, current_deepth + 1)
```